1. Field of the Invention
The present invention relates to alumina hydrate particles, an alumina hydrate particle dispersion sol, and a coating liquid for forming an ink receptive layer wherein the alumina hydrate particles are contained. More particularly, the present invention relates to highly transparent alumina hydrate particles which contain alkali metal oxide and ammonia components in extremely minute amounts and which, when dispersed in water, exhibit a low viscosity, and further relates to a sol wherein the alumina hydrate particles are dispersed, to a coating liquid for forming an ink receptive layer wherein the alumina hydrate particles are contained, and to a substrate with ink receptive layer obtained from the coating liquid.
2. Description of the Prior Art
Fine particles of a metal oxide such as silica, alumina or alumina hydrate, fine particles of a metal hydroxide and sols obtained by dispersing these in solvents have been used in various fields. For example, there can be mentioned uses in a catalyst, a catalyst support, a material for film formation, a filler incorporated in a resin, various binders, a slip improver, a lubricant, a thickener, cosmetic ingredients, etc.
Recently, there is an increasing expectation for the use of alumina or alumina hydrate particles for formation of a receptive layer on a printing recording medium. For example, it is described in Japanese Patent Publication No. 3(1991)-24906 that a recording medium having a receptive layer wherein a cationic hydrated aluminum oxide is contained is highly suitable for printing with a water soluble dye ink.
It is further described in Japanese Patent Publication No. 4 (1992)-115984 that a recording sheet comprising a layer of pseudoboehmite alumina and, superimposed thereon, a layer of porous silica is highly transparent and exhibits high ink absorbency.
It is still further described in Japanese Patent Laid-open Publication No. 6(1994)-55829 that a recording sheet comprising a layer of porous silica particles having an average particle diameter of 2 to 50 μm, an average pore diameter of 8 to 50 nm and a pore volume of 0.8 to 2.5 cc/g and, superimposed thereon, a porous layer of pseudoboehmite obtained by drying alumina sol exhibits high ink absorbency and is excellent in pigment stability.
On the other hand, the inventors proposed in Japanese Patent Application No. 10(1998)-206284 a recording sheet with ink receptive layer prepared using a coating liquid for forming an ink receptive layer which contained oxide particles of positive ζ-potential carrying on their surfaces a cationic hydrated metal compound, in particular, containing Al3+ as a metal cation. The recording sheet was described as being free from blotting, enabling clear printing, and being excellent in water resistance, weather resistance, fading tendency, etc.
However, when conventional alumina particles of small pore diameter or small pore volume are employed, although pigment stability is excellent, the ink absorption speed is low and also the ink absorption capacity is small, so that blotting and unclearness have been experienced.
Moreover, the average pore diameter of alumina and alumina hydrate particles is generally in the range of about 5 to 15 nm, and it is difficult to obtain those of greater pore diameter. Even if those were obtained, the pore volume would be unfavorably small, and there would occur the problem of economic inefficiency caused by, for example, the need for post-treatment and special technique.
Further, with respect to the conventional alumina sol or alumina hydrate particle dispersion sol, the viscosity is high and the particles are likely to aggregate together, so that various problems have been posed. For example, it is difficult to prepare a high-concentration sol wherein the concentration of Al2O3 is about 8% by weight or greater, thereby necessitating transportation of a low-concentration sol. This would increase transportation cost. In the aforementioned uses, the preparation of a low-concentration sol only would, for example, disenable forming a thick coating because of the low concentration at the time of coating formation. For increasing the coating thickness, it would unfavorably be needed to repeat application and drying of a coating liquid.
Still further, even if a high-concentration sol is prepared from conventional alumina or alumina hydrate particles, there have been problems such that the transparency of the sol is poor and that the viscosity of the sol is extremely high.
In particular, it has been difficult to obtain a sol of high transparency and low viscosity from porous alumina.
The present invention has been made with a view toward solving the above problems of the prior art. In overcoming these problems, the present invention provides alumina hydrate particles and a process for producing same wherein the particles have a large pore volume and have a pore diameter which falls in a specified range, and, in addition, provides a highly transparent alumina hydrate particle dispersion sol which, even if in a high concentration, exhibits a low viscosity.
The present invention further provides a coating liquid for forming an ink receptive layer wherein the above alumina hydrate particles are contained, and provides a substrate with an ink receptive layer formed with the use of the coating liquid.